MC68HC908EY16 Datasheet, PDF (107/278 Pages) Motorola, Inc – Microcontrollers

Functional Description
INTERNAL BUS
KBD0
TO PULLUP
.
ENABLE
.
KB0IE
.
KBD4
TO PULLUP
ENABLE
KB4IE
V_DD
CLR
D
Q
CK
ACKK
RESET
VECTOR FETCH
DECODER
KEYF
SYNCHRONIZER
MODEK
KEYBOARD
INTERRUPT FF
IMASKK
Figure 10-2. Keyboard Module Block Diagram
KEYBOARD
INTERRUPT
REQUEST
The vector fetch or software clear and the return of all enabled keyboard interrupt pins to logic 1 may occur
in any order.
If the MODEK bit is clear, the keyboard interrupt pin is falling edge-sensitive only. With MODEK clear, a
vector fetch or software clear immediately clears the keyboard interrupt request.
Reset clears the keyboard interrupt request and the MODEK bit, clearing the interrupt request even if a
keyboard interrupt pin stays at logic 0.
The keyboard flag bit (KEYF) in the keyboard status and control register can be used to see if a pending
interrupt exists. The KEYF bit is not affected by the keyboard interrupt mask bit (IMASKK) which makes
it useful in applications where polling is preferred.
To determine the logic level on a keyboard interrupt pin, use the data direction register to configure the
pin as an input and read the data register.
NOTE
Setting a keyboard interrupt enable bit (KBIEx) forces the corresponding
keyboard interrupt pin to be an input, overriding the data direction register.
However, the data direction register bit must be a 0 for software to read the
pin.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
107